1. Field of the Invention
The present invention relates to guiding endoscopic procedures, and more particularly to guiding a flexible instrument.
2. Discussion of Related Art
Transbronchial needle aspiration (TBNA) is a valuable minimally invasive procedure in the bronchoscopic diagnosis and staging of patients with lung cancer. The procedure allows nonsurgical access to lymph nodes from the inside of the tracheobronchial tree. Typically, a biopsy can be performed by maneuvering a bronchoscope to a desired site within the tracheobronchial tree. The surgeon can insert a tool, for example, a needle, through the bronchoscope and puncture the bronchial wall to hit a target behind, e.g., a tumor. This is literally a “blind” puncture since the target object is at no time visible through the bronchoscope. To increase the chance of hitting the target, a surgeon may take more than one tissue sample for every biopsy. Studies have shown that up to eight needle aspirations in the same site can be safely performed. However, there is no strategy for placing the aspirations other then a trial-and-error approach.
Despite the fact that the surgeon can perform more than one needle aspiration in a single biopsy, this procedure has a failure rate of about 60 to 80%, if the bronchial wall is not yet affected. The blind nature of the procedure and the physician's lack of confidence about where to position the needle are obstacles to the widespread use and positive diagnostic yield of TBNA. Performing a TBNA can include three-dimensional (3D) imagination (coordination of the learned three dimensional anatomy with a fish-eye distorted 2D video image) together with the handling of the endoscope (hand-eye-coordination).
Techniques used to guide TBNA can be classified into three different groups: imaging based technology, on-line visualization of the target and tracking of the bronchoscope.
Imaging based techniques can include, for example, fluoroscopy, CT and CT fluoroscopy. These techniques can show the endoscope, the advanced needle and the target lesion. Fluoroscopy produces a real-time two-dimensional image projection with poor contrast. Typically, the target lesion is not visible. Conventional CT produces images of adequate quality but the procedure can be cumbersome and time consuming since real-time imaging may not be possible and each sequence needs to be prescribed in advance. CT fluoroscopy is a term for continuous-imaging CT that allows the visualization of dynamic processes in real-time, like the insertion of a needle into the target lesion. However, this technique is limited to axial images and may need significant CT-scanner time and relatively high radiation dosage.
On-line visualization can include, for example, techniques that visualize the target lesion by inserting an ultrasound transducer through a working channel of the bronchoscope. There is no significant difference in sensitivity compared to unguided TBNA.
Tracking methods can include techniques that track the tip of the bronchoscope in real-time to guide the TBNA. For example, tracking the bronchoscope's tip by processing the endoscope images. The Biosense intra-body navigation system uses electromagnetic fields to track a sensor that can be attached to the bronchoscope's tip. In an in vivo study, ten to twenty markers were secured on a test subject's chest and the respiratory motion was monitored using a second sensor to compensate for breathing motion. The study showed an accuracy of 4.2 mm+−2.6 mm (+−SD).
However, no known system or method exists for guiding a flexible instrument using predetermined models. Therefore, a need exists for a method of blindly guiding a flexible instrument according to a predetermined patient specific model.